Proximity fuze antenna



1964 A. H. DELL ETAL 3,143,072

PROXIMITY FUZE ANTENNA Filed April 19, 1948 2 Sheets-Sheet 2 FIG. 7

RE Choke INVENTORS ALBERT H. DELL JOHN H. KUCK BY JULES H. SREB ATTORNEY United States Patent 3,143,072 PROXIMITY FUZE ANTENNA. Albert H. Dell, Cheverly, Md., and John H. Kuck and Jules H. Sreb, Washington, D.C., assiwors to the United States of America as represented by the Secretary of the Navy Filed Apr. 19, 1948, Ser. No. 21,868 6 Claims. (Cl. 102-70.2)

This invention relates to a combined loop antenna and inductance for proximity fuzes for missiles and for other purposes involving ultra-high frequency oscillations.

An object of the invention is to provide a loop antenna of small size that may be incorporated in a fuze of the customary dimensions, to serve in place of the conventional dipole antenna.

Another object of the invention is to provide capacitors in the antenna loop that may be adjusted very precisely to the desired values of capacitance, and that may be duplicated readily by manufacturing methods, on a large scale.

Still another object of the invention is to provide a fuze having a loop-type antenna wherein a single loop fulfills simultaneously the functions of both antenna and tank circuit. This affords the advantage that the radio frequency loading of the oscillator is independent of the size of the missile, so that one standardized type of fuze may be used interchangeably for all sizes of missiles. This feature also prevents modulation of the fuze by streams of ionized combustion products leaving the tail of the projectile, when the latter includes a rocket or ram jet.

Another advantage of this independence of the fuze on the projectile size is that it makes it possible to use frequency ranges which are not available to conventional, open-antenna, fuzes because of the unsuitable radiation patterns the latter would possess.

The longitudinal loop is advantageous when sensitivity in the forward direction is desired. The reason is that such loops have radiation patterns with large lobes extending forward, whereas the open-antenna fuzes lack extensive forward lobes. This feature is advantageous for high-angle howitzer and mortar fire, and bombing, but is not well suited for anti-aircraft fire because the fuzes would fire prematurely.

A further object of the invention is to make the oscillator loop as a unit, free from electrical joints and very stable, both mechanically and electrically. This object is attained by making the loop of two strips of metal foil, each permanently joined at a respective end to the corresponding end of the other, by a layer or insert of dielectric material, so that two capacitors are thus formed, mechanically integral with the strips of foil, the entire loop thus consisting electrically of two inductances and two capacitors, located in alternation and so connected that one capacitor is in series with the two inductances while the other is a shunt capacitor.

These modes of insertion of the capacitors in series and in parallel make it possible to adjust independently the frequency and loading of the loop. It will be understood that the parallel capacitor is at the input end of the loop, and thus in parallel with the oscillation generator.

Another object of the invention is to provide a type of construction that makes it possible to adjust the values of the two loop capacitors quickly and easily by trimming with shears, to arrive at the exact magnitudes that give the best results, and which are then capable of exact duplication on a production basis.

And another object is to provide a transverse loop oscillator fuze wherein symmetry in the electrical characteristics of the loop is attained by the provision of two oscillator tubes, that yields automatic balancing and does not require the use of balancing capacitors.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a side elevation of a longitudinal-loop fuze, with the case in central axial section, a fragment of the shell being also shown;

FIG. 2 is an enlarged axial section of the said fuze, along line 22 of FIG. 1;

FIG. 3 is an enlarged axial section of the fuze, along line 3-3 of FIG. 2;

FIG. 4 is a cross section of the fuze along line 4-4 of FIG. 2, and still more enlarged;

FIG. 5 is a circuit diagram for the longitudinal-loop fuze;

FIG. 6 is an elevation view of a fuze having a transverse loop;

FIG. 7 is a plan view of the fuze in FIG. 6 on a much larger scale;

FIG. 8 is an elevation view partly broken away, and partly in section on broken line 88 of FIG. 7; and

FIG. 9 is a circuit diagram for the transverse-loop fuze.

The present invention provides a loop antenna. Heretofore, it was customary, as stated, to use dipole antennae in proximity fuzes. Such antennae usually consisted of wires, or of sheet metal, either embedded within the material of the plastic casing of the fuze, or located on its inner or outer surface.

This invention provides frequency ranges of operation that would be barred from the dipole fuze because of the unfavorable distribution pattern of the latter, and also makes it possible to design a single standardized oscillator for use in various sizes of projectiles.

The construction wherein the capacitors form integral parts of the loop provides an advantage over loop fuze designs wherein separate capacitor units are soldered into the loop, in that it avoids the production difficulties of soldering to the loop, which would abstract heat rapidly tom the soldering iron, and it also avoids the added inductance of small capacitor leads, to which the operation of the circuit is likely to be extremely critical. In addition, the new loop structure provides a very compact, space-saving arrangement.

Another very important advantage of the invention is that by building the capacitors into the loop itself in place of the formerly common use of separate ready-made units, it is possible to adjust the capacitances precisely to attain a desired wave length and loading, by the simple expedient of making the capacitors a little too large initially, and then trimming them to proper size with shears.

Referring now to FIGS. 1, 2 and 3, the structure of one form of the oscillator loop is shown. Here the loop consists electrically of two pieces of copper ribbon strips 1 and 2, the upper end portions 3 and 4 thereof being bent down and into parallelism as shown, with a sheet or layer of dielectric material 5, such as polyethylene, cemented or fused between them. This material 5 acts to bond the two ends 3 and 4 of ribbon strips 1 and 2 firmly to one another, and thus forms a capacitor therewith.

The loop here is illustrated as of a general hexagonal shape, the upper side of the hexagon being formed by the two arcuate upper ends of the loop and the three lower sides of the said hexagon being formed by portions 6, 7, 8 and 9 of strips 1 and 2.

Between portions 8 and 9 the lower terminal parts of the strips 1 and 2 are bent upwardly at an angle, as shown at 16) and 11 respectively, with a layer of dielectric material12 between portions and 11, thus forming a second built-in capacitor at the lower end of the loop.

Referring next to the circuit diagram in FIG. 5, it will be seen that a wire 14 is soldered or otherwise electrically connected to strip 1 at its upper end 13. A radio frequency choke 15 is interposed in this conductor 14 as indicated, to keep the radio-frequency energy from being dissipated through the direct current portions of the circuit.

The particular circuit illustrated in FIG. 5 shows the other end of choke 15 grounded through conductor 16 to a shield can 18 of the fuze and thus grounded also to the shell on which the fuze is mounted.

one side of filament 25, while the companion winding 27 is in the other filament lead 28, so that the high- ,frequency energy is kept out of the batteries. Another radio-frequency choke 29 serves the same purpose in lead 30, which supplies the B+ connection to conductor 23.

The oscillator loop 1, 2 is preferably mounted on a support 31 best known in FIG. 2. This support is made v of suitable insulating material, such as polystyrene, polyethylene, or the like, that has good high-frequency dielectric characteristics, to avoid losses. An opening 32 in'this support provides room for other components of the oscillation circuit, as shown.

The metal vessel 18, known as the shield can, serves as a base for the support 31, and has the additional purpose of shielding its own contents electrostatically. The oscillator tube 22 is accommodated in this shield, and is surrounded by the protective sleeve 33, made of rubber,

or equivalent shock-absorbing protective material. This sleeve is surrounded by the closed-end metal tube 34, carried by the top 17 of the shield can 18, as shown best in FIG. 3. Incidentally, resistor 40 and conductors and 41 are housed in the shield can. A suitable base 35, provided with prongs 36, that may be engaged in a corresponding socket, is attached to the bottom flange 37 of the shield can in any preferred way, for instance, by the pins 38. The base has a central opening 39 through which access may be had to the interior of the can 18.

In addition to the capacitors already mentioned, there are two others. Actually, both are formed by the same dielectric sheet 19, between the top 17 of the shield can and the portions 8 and 9 respectively of strips 1 and 2, but in the circuit these two capacitors constitute separate components. These act as balancing condensers, and their values may be adjusted by proper selection of the location of the capacitor 10, 11, 12, because obviously the two balancing capacitors change in opposite senses as such location is shifted.

The balancing capacitors serve the function of preventing excitation of the shell, that otherwise might occur, due to unbalance. This is important in eliminating dependence of the fuze on shell sizes, and rocket or other flames. The same feature, incidentally, may be secured by a transverse loop antenna or by a two-tube excited longitudinal loop antenna, in both cases due to the circuit symmetry inherent therein, which obviates the need for balancing capacitors.

While each of the two capacitors 3, 4, 5 and 1t), 11, 12 in an electrical sense consists only of two sheets of metal foil with a sheet of dielectric material between them, yet in the actual manufacture of these capacitors a sandwic is formed by interleaving the twometal sheets between three sheets of polyethylene or equivalent thermoplastic material, and applying heat and pressure until all five sheets become firmly bound together. This provides each capacitor with a firmly adherent outer covering of the dielectric on each face, and thus facilitates cementing the same rigidly into the support 31. This result would be relatively difficult to secure without such coatings.

The operation of the circuit does not differ from that of any conventional oscillator, and hence needs no di cussion. One advantage of the new structure however is that there are no joints in the loop, which is made of two strips, each continuous from end to end. The end portions of these strips are themselves the capacitor electrodes and thus even the capacitors are continuous with the strips.

The capacitances may be adjusted with extreme closeness, by trimming off small portions until the desired values are reached. Thebalancing capacitors likewise are associated with the loop without needing any joints, since they are formed between the grounded top of the shield can and portions of the loop itself. This gives flexibility of design, the ability to change the frequency and loading in production, without altering the mechanical design, but by merely changing the values of these capacitors. I

Since there is no soldered or other joint in the loop,

,which is the main part of the radio-frequency tank circuit, no defect or variation therein can result from poor .soldering or from deterioration of initially good joints,

.sistance joints are present, and high-quality, low-loss insulating material is used as the dielectric of the various capacitors.

Referring now to FIGS. 6-9, inclusive, there is illustrated a modified form of the invention in which the loop is located transversely of the projectile instead of in an axial plane. 7

This form has a support 42 of suitable dielectric material, such as polystyrene, polyethylene, or the like,

.that serves to hold the various circuit components in position. A cylindrical loop 43 surrounds support 42 and :is held by upper end of the support 42.

The support 42 is, in turn, supported by a base section 45, preferably of metal, with a suitable flange 44 extending transversely thereof, for mounting the fuze casing,

' and for other purposes. A cylindrical can or casing 46 is provided within the support 42 as shown, and its purpose is to accommodate and electrostatically shield the amplifier components of the fuze, which are not shown. The usual pin-type base 47 is secured to the end of the base section 45, to provide the requisite electrical connections to the batteries and other devices of the fuze.

Referring more particularly to FIG. 9, it will be noted that the circuit illustrated presents mirror-symmetry about a vertical center line. This is done to provide a circuit that is as nearly balanced as possible, so that the shell or other missile will not disturb the radiation pattern when the fuze is applied thereto. This makes it possible to disregard the electrical characteristics of the missile, that is, a single type of fuse may be used for any missile.

The desired symmetry is attained by providing the oscillator tubes in duplicate. Two electronic tubes 48 and 49 have their anodes 50 and 51, respectively, con nected in common to the terminal of the B-battery as shown, through the central conductor 52 of the coaxial cable 53. The grids 54 and 55 are connected to suitably located points 56 and 57, respectively, of the loop 43,

through wires 58 and 59. The cathode filaments 60 and 61 are heated by the A-battery, through bifilar radiofrequency chokes 62 and 63, with coaxial cables 64 and 65 being used for the connections.

The negative terminals of the A- and B-batteries are connected together and grounded through conductor 66 at terminal 66a. Suitable connections are also made to the loop at points 69 and 70 through conductors 71 and 72, with radio frequency chokes 67 and 68 being interposed as shown.

Capacitors are formed at 73 and 74 by interleaving a dielectric with the ends of the half-loops, bent radially inward as shown. These capacitors are made in the same way as those in the longitudinal loop, already described, and they may be adjusted in exactly the same manner, by trimming them with shears.

Two types of loop have now been disclosed in detail. They have in common the feature that their electrical characteristics are capable of close adjustment, by reason of the capacitor structures that permit trimming. They have in common also the feature that each type of loop provides a tank circuit that is of high Q and is stable both in the electrical and the mechanical sense, thus fitting it for mass production and storage.

The two types of loop differ in their radiation patterns, for obviously the longitudinal loop has a pattern that varies in different directions radially of the fuze axis, while the transverse loop is located symmetrically and provides a substantially uniform pattern, that does not vary as the missile spins. This latter pattern is, therefore, not easily disturbed by the metal of the missile, as it is initially well balanced and substantially remains so, regardless of the nature and size of the missile to which the fuze is applied.

While it is true that, because of the small size of the antenna, a loop oscillator fuze has lower sensitivity, in comparison with that of the conventional fuze, this may be compensated by providing a more sensitive amplifier.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. In a radio proximity fuze for a projectile, said fuze having a metallic shield can, a loop antenna comprising two elements, each consisting of a strip of sheet metal, said strips being bent to have one pair of corresponding ends adjacent and substantially parallel with each other, a sheet of dielectric material between said ends, parts of the remaining corresponding ends of the strips being bent into substantial parallelism with a portion of the shield can, and a sheet of dielectric material between said respective parts and the shield can, whereby three capacitors are formed, one between the two strips, and the other two each being one of the strips and the shield can, the two last-mentioned capacitors balancing the radio-frequency potentials of said two elements, whereby radiation from the projectile due to undesired excitation thereof from the antenna is substantially eliminated.

2. The structure defined in claim 1, with the addition of a fourth capacitor consisting of the corresponding ends of the strips near the shield can and a sheet of dielectric material between them.

3. In a radio proximity fuze for a projectile, a generator of radiant energy, comprising a circular loop having its plane transversely arranged with respect to the axis of said projectile, said loop being divided into two symmetrically located semicircular halves having their end portions overlapping, a dielectric at each end of each such half, thus forming two capacitors integral with said loop and diametrically opposite one another, and symmetrically arranged oscillator circuits coupled with the respective halves of said loop to provide mutually balanced radiation from said halves, whereby the projectile is not subjected to undesired excitation from said generator due to any unbalance in the oscillator circuits.

4. In a radio proximity fuze for a projectile, a generator of radiant energy, comprising, an antenna loop, said loop being divided into two approximately symmetrically located halves having their end portions overlapping, a dielectric at each end of each such half, thus forming two capacitors integral with the loop and diametrically opposite one another, and oscillator oircuits coupled with the respective halves of said loop to provide mutually balanced radiation from said halves, whereby said projectile is not subjected to undesired excitation from said generator due to any unbalance in the oscillator circuits.

5. An arrangement as set forth in claim 4, wherein the plane of said antenna loop is arranged transversely with respect to the longitudinal axis of the projectile.

6. An arrangement as set forth in claim 4, wherein the plane of said antenna loop is arranged substantially axially of said projectile.

References Cited in the file of this patent UNITED STATES PATENTS 2,137,598 Vos Nov. 22, 1938 2,311,872 Rote Feb. 23, 1943 2,390,784 Drobish et a1 Dec. 11, 1945 2,395,442 Ballard Feb. 26, 1946 2,411,788 Hammond Nov. 26, 1946 FOREIGN PATENTS 573,621 Great Britain Nov. 29, 1945 

4. IN A RADIO PROXIMITY FUZE FOR A PROJECTILE, A GENERATOR OF RADIANT ENERGY, COMPRISING, AN ANTENNA LOOP, SAID LOOP BEING DIVIDED INTO TWO APPROXIMATELY SYMMETRICALLY LOCATED HALVES HAVING THEIR END PORTIONS OVERLAPPING, A DIELECTRIC AT EACH END OF SUCH HALF, THUS FORMING TWO CAPACITORS INTEGRAL WITH THE LOOP AND DIAMETRICALLY OPPOSITE ONE ANOTHER, AND OSCILLATOR CIRCUITS COUPLED WITH THE RESPECTIVE HALVES OF SAID LOOP TO PROVIDE MUTUALLY BALANCED RADIATION FROM SAID HALVES, WHEREBY SAID PROJECTILE IS NOT SUBJECTED TO UNDESIRED EXCITATION FROM SAID GENERATOR DUE TO ANY UNBALANCE IN THE OSCILLATOR CIRCUITS. 